Russia's 2014 World Cup squad were subject to extra doping tests, former FIFA chief medical officer Jiri Dvorak told BBC Sport.
Dvorak said the tests adhered to correct procedures and were carried out because of rumours about Russian athletes, but they came back negative.
"We heard some rumours about xenon in Russia, so we decided to test that," Dvorak said.
"We just tested the Russian team for that because the substance was unknown in the rest of the world. All tests were negative."
Xenon, a gas...